As is known, helicopters are normally equipped with a number of transmissions for transmitting motion from one or more turbines to the main and/or tail rotor, and/or from the turbine to a number of accessory devices, i.e. for powering on-board equipment, for example.
The transmissions normally comprise one or more rotary members rotating about respective axes; a casing housing the rotary members; a number of bearings supporting the rotary members in rotary and axially-fixed manner inside the casing; and a feed device for supplying and lubricating the bearings with lubricating oil contained inside special tanks.
In the event of damage to the tank or breakdown of the feed device, the oil pressure falls, thus preventing operation of the transmission.
In the industry, a need is felt to ensure, in such cases, correct operation of the transmission for a predetermined length of time, e.g. thirty minutes, to allow the helicopter to land.
Moreover, for missions of a given duration, helicopter certification regulations require that the helicopter be able to maintain level flight for said predetermined length of time.